Manifold Pressure Sensor MPS and timing, what is the effect on timing? Options

[thompson-mfr]

Ok, I will try and keep this as brief as I can.

I will pose the question before providing the background.

?? What, if any, effect does the MPS have to do with actual timing of the motor??



Now for the reason for my question.

1974 2.0L FI

My MPS (0 280 100 019 adjusted VW T4 unit) randomly stopped working properly even though electrically it checks out and holds vacuum. Maybe an aneroid cell? anyway not sure. I then started trouble shooting thinking it was points, plug wires, etc. ( I replaced to be sure) and readjusted the timing and dwel.

Right after the MPS stopped working I found a good deal on another nice '74 2.0 FI 914. It has a factory MPS correct PN 0280 100 043 and runs perfectly.

So, I thought I would swap MPS's and see if this fixed my problem. It didn't run well.

Thoughts?? I have read Pbanders a bunch of times.

I have included a picture of the new car in hopes there are others like me that like pictures. I only open threads with pictures as I cannot read good (well )just joking). Maybe other people can relate to this.

[SLITS]

MPS has no effect on engine timing.

It only determines, in combo with the ECU and other sensors, the length of injection pulses.

[ThinAir]

Since you were running a non-stock, adjusted, MPS - are you running the stock CHT?

On my '73 I found that I could run both the 037 and 043 MPS units with the stock 017 CHT, but after I changed to a new 012 CHT the 043 MPS would idle evenly for a few moments, then the engine would die.

See this thread for the long story. I may have had MPS issues (or MPS / spark plug placement issues), but ultimately it turned out to be something in my distributor.

[thompson-mfr]

Since you were running a non-stock, adjusted, MPS - are you running the stock CHT?

On my '73 I found that I could run both the 037 and 043 MPS units with the stock 017 CHT, but after I changed to a new 012 CHT the 043 MPS would idle evenly for a few moments, then the engine would die.

See this thread for the long story. I may have had MPS issues (or MPS / spark plug placement issues), but ultimately it turned out to be something in my distributor.

I am running a stock 2.0l CHT. I had to adjust the 019 T4 unit to get it to run right (last one). Was running great with really good power.

This was a good suggestion. Maybe I will replace the CHT to be sure.

I just put another T4 MPS (PO had a box of them) and adjusted it to run good(currently).

[brant]

I hope your using a wideband o2 sensor to adjust these.
I have seen with my own eye's on the sensor that you can not tune these by feel or ear. The adjustment is way to sensative.

[thompson-mfr]

I hope your using a wideband o2 sensor to adjust these.
I have seen with my own eye's on the sensor that you can not tune these by feel or ear. The adjustment is way to sensative.

No I do the guess and check method. Adjust a little then drive....adjust a little then drive. I only adjust the small inner screw. The full load stop is drilled out in the middle.

I don't have a wideband o2 sensor reader, or are you talking about taking the voltage from a single wire o2 sensor?

Please tell me how you do it. I would like to avoid buying any more expensive measuring equipment if possible.

[brant]

I'm sorry I was talking about a wideband 02 sensor
perhaps there is someone in Oregon that will loan one to you or help out for 30 minutes and the price of a beer

On the wideband, I could see where an 8th turn of the screw was the difference between way too rich and way too lean
its a really really sensitive adjustment, and there are 2 seperate adjusments (2 screws)

brant

[SLITS]

For $3 off the net from China, you can buy a digital volt meter. It's a 3 wire setup .. ground, B+ and signal.

The single wire sensor puts reads 0 - 1 volt. Interpreting the voltage readings to A/F ratio, I would have to ask a friend as he just installed one in his car.

[thompson-mfr]

I'm sorry I was talking about a wideband 02 sensor
perhaps there is someone in Oregon that will loan one to you or help out for 30 minutes and the price of a beer

On the wideband, I could see where an 8th turn of the screw was the difference between way too rich and way too lean
its a really really sensitive adjustment, and there are 2 seperate adjusments (2 screws)

brant

yeah, I have attempted to adjust the 019 T4 MPS the same as the good 043 MPS with an LCR meter and it cannot match. The internals of the T4 MPS must be a little different. I have heard this from other sources.

Do you use an in cockpit one or a meter style. Maybe I need to breakdown and spend the $$$. I have seen them for $170 and then the cost of an o2 sensor. Does this seem right?

[thompson-mfr]

For $3 off the net from China, you can buy a digital volt meter. It's a 3 wire setup .. ground, B+ and signal.

The single wire sensor puts reads 0 - 1 volt. Interpreting the voltage readings to A/F ratio, I would have to ask a friend as he just installed one in his car.

can you explain further. I would need a 3 wire o2 sensor and then measure the voltage with a multimeter?

I have several digital voltmeters, dwell, and LCR (Inductance), just not wideband o2

[SLITS]

For $3 off the net from China, you can buy a digital volt meter. It's a 3 wire setup .. ground, B+ and signal.

The single wire sensor puts reads 0 - 1 volt. Interpreting the voltage readings to A/F ratio, I would have to ask a friend as he just installed one in his car.

can you explain further. I would need a 3 wire o2 sensor and then measure the voltage with a multimeter?

I have several digital voltmeters, dwell, and LCR (Inductance), just not wideband o2

He had the Edelbrock multiwire set up. When it broke he went to a single wire O2 sensor and hooked up the digital voltage meter to it. The mini DVM came as a 3 wire ... red (supply voltage, minimum 5 volts), Black (ground) and Blue (signal) which was wired to the O2 sensor. All I know is that the readings from the O2 sensor vary from 0 - 1 volt. I'll ask him what the volt range he sees on the meter means as far as A/F ratio.

[Krieger]

You can buy a cheap a/f meter from JEGS for $50. It may make more sense and easier to read when your driving.

[Dave_Darling]

For $3 off the net from China, you can buy a digital volt meter. It's a 3 wire setup .. ground, B+ and signal.

That is a narrow-band setup, and it is effectively useless for tuning. Mostly what it tells you is the temperature of the sensor, and even that has a lot of error.

The wide-band O2 meter can be used to check your mixture. The narrow-band one only lets a modern FI control the mixture to where the catalytic converter works well.

How can you tell if it's wide-band or narrow-band? If it doesn't say wide-band, it's narrow. If it costs a reasonable amount of money, it's narrow-band.

--DD

[Bleyseng]

If you plugged in a stock 043 MPS into a 74 2.0l FI setup and had to adjust it to run then something is wrong with you setup.

Now that you have adjust the MPS by drilling it out you have to use a wide band to get the A/F ratio correct or ship it to someone who has a Waveteck meter and can reset the 043 to spec.
Then fix what ever is wrong with your FI.

[thompson-mfr]

If you plugged in a stock 043 MPS into a 74 2.0l FI setup and had to adjust it to run then something is wrong with you setup.

Now that you have adjust the MPS by drilling it out you have to use a wide band to get the A/F ratio correct or ship it to someone who has a Waveteck meter and can reset the 043 to spec.
Then fix what ever is wrong with your FI.

I did not adjust the 043 MPS. I simply put a good one in my other car and it didn't run well.

I only adjusted the 019 T4 VW MPS unit. I have it running "OK" with the 019 T4 VW MPS. I may get a A/F meter and dial it in more.

I find it very strange the factory 043 MPS does not work well in my car????!!!

[SLITS]

I find it very strange the factory 043 MPS does not work well in my car????!!!

What ECU do you have? To match up, it should be an 052.

[thompson-mfr]

I find it very strange the factory 043 MPS does not work well in my car????!!!

What ECU do you have? To match up, it should be an 052.

I need to double check that. I thought I had double checked that before, but cannot remember. That or the CHT is a possibility.

I have never run a 043 MPS correct to my 2.0L, so don't have that as a reference.